US2677779A - Tricolor kinescope magnetic shield - Google Patents

Description

May 4, 1954 H. c. GooDRlcl-l.

TRICOLOR KINESCOPE MAGNETIC SHIELD 2 Sheets-Sheet l Filed May 22, 1955 INI/ENTOR. IIUNIEHE. EnnDmm-I May 4, 1954 H. c. GOODMCH 2,677,779

TRICOLOR KINESCOPE` MAGNETIC SHIELD Filed May 22, 1953 2 Sheets-Sheet 2 INI/ENTOR.

HUNTER E. EDDDRICH Patented May 4, 1954 TRICLOR KINESCOPE MAGNETIC SHIELD Hunter C. Goodrich, Collingswood, N. J., assignor to Radio Corporation of America, a corporation oi Delaware Application May 22, 1953, Serial No. 356,620

This invention relates to systems for controlling the electron beams of cathode ray tubes and particularly to systems in which a plurality of beams is deflected by a common deection apparatus.

One type of cathode ray tube with which the present invention may be successfully employed is a color kinescope of the general type described in an article titled A Three-Gun Shadow-Mask Color Kinescope, by H. B. Law published in the ent angles, the angle of impingement determining c the particular color of the light produced by the phosphor areas. The invention also pertains to a kinescope of the type described in another article titled A One-Gun Shadow-Mask Color Kinescope, by R. R. LaW, published in the Proceedings of the I. R. E., vol. 39, No. 10, October 1951 at page 1194. Such a tube is the subject matter of a copending U. S. patent application of Russel R. LaW, Serial No. 165,552, led June l, 1950, and titled Color Television.

It is necessary for the satisfactory operation of such kinescopes to effect substantial convergence of the diiierent electron beam components at all points of the raster scanned thereby in the plane of the target electrode. In general, this convergence may be eifected by means of apparatus such as that disclosed in an article titled Deflection and Convergence in Color Kinescopes by A. W. Friend, published in the Proceedings of the I. R. vol. 39, No. 10, October 1951 at page 1249. One such system in accordance with the disclosure of this article forms the subject matter of a copending application of Albert F. Friend, Serial No. 164,444 filed May` 26, 1950, and titled Electron Beam Controlling System. Such beam convergence apparatus includes an electron-optical system by which to control the beam convergence angles. The electron-optical system is variably energized as a function of the radial angle of beam deflection.

Another type of apparatus for controlling the convergence of a plurality of electron beam compcnents in a predetermined plane and with which the present invention is more particularly concerned comprises, in general, a means for pro- 7 Claims. (Cl. 313-70) ducing a plurality of electron beam components which traverse predeiiection paths that are spaced respectively about the longitudinal axis of the tube, and individual electromagnetic means located respectively adjacent to the pre-deection beam paths and of such a character to be energizable directly from the beam deection circuits in a manner to efect the desired beam convergence. In this manner, the beam convergence angle may be varied in a manner suitable to maintain the desired beam convergence in the predetermined plane at all points in the scanned raster.

More particularly, it will be understood that the term beam components as used in this specncation and in the appended claims denotes either a plurality of individual electron beams emanating, respectively, from a plurality of electron guns or from a single electron gun provided with suitable electron-optical, or other apparatus, for forming three individual beams and, in addition, those components of a single electron beam to which is imparted a spinning motion so as to trace a substantially conic locus at different positions thereof. Accordingly, the apparatus by which a plurality of such electron beam components is produced may include on the one hand, three electron guns or, on the other hand, a single electron gun, together with the auxiliary apparatus by which the spinning motion is imparted to the beam.

rI'he particular beam convergence electromagnetic apparatus to which this invention pertains includes for each beam component a pair of pole pieces located internally of the kinescope envelope. It has been found that magnetic uX leaking from the deflection yoke traverses the various pairs of pole pieces diiferently, thereby tending to cause a misconvergence of the beam components.

It, therefore, is an object of the present invention to prevent leakage fiux from a rasterscanning deiiection yoke from affecting individual beam-convergence electromagnets in a manner to cause misconvergence of a plurality of beam components.

Another object of the invention is to magnetically shield a plurality of individual beamconvergence electromagnets located in a predeection region of a plurality of beam components from a raster-scanning deflection yoke.

In accordance with this invention, multi-beam cathode ray tube apparatus, having a plurality 3 with a magnetic shield located between the beam deflection apparatus and the beam convergence apparatus to exclude from the latter leakage flux 'from the former.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as Well as additional objects and advantages thereof, will best be understood from the following description when read in conjunction with the accompanying drawings.

In the drawings:

Figure l is a view showing the general arrangement of image-reproducing apparatus embodying one form of an electron beam convergence system in accordance with this invention;

Figure 2 is a transverse crosssectional view taken generally on the line 2-2 of Figure i and showing the arrangement of the beamconvergence electromagnets;

Figure 3 is another transverse cross-sectional view taken generally along the line 3-3 oi Figure l and showing a form of magnetic shielding apparatus in accordance with the invention; and,

Figure 4 is a schematic circuit diagram oi an arrangement in accordance with the invention for energizing the electromagnetic beam con vergence apparatus.

Reference rst will be made to Figure l for a general description of an illustrative enih-odi ment of electron beam convergence system in accordance with 'the present invention. The sys* tem includes a tri-color kine'scope i! which may be of the same general type as that disclosed in the H. B. Law paper previously referred to. It will be understood, however, that the ltinescope alternatively, may be of other types such as that shown in the R. R. Law paper. In either case, however, the kinescope preferably has a substantially flat luminescent screen I2 provided with a multiplicity of small phosphor areas arranged in groups and capable respectively of producing light of the different primary colors in which the image is to be reproduced when excited'by an electron beam. In back of and spaced from the screen l2 there is an apertured masking electrode I3 having an aperture for and in alignment with each group of phosphor areas cf the screen I2.

In the particular tube illustrated, the kine-- scope also has a plurality of electron guns, equal in number to the number of primary colors in which the image is to be reproduced. Each of these guns may be conventional, consisting of a cathode, a control grid and a focussing electrode. Since the three-guns are identical, the different parts thereof will be referred to collectively as the cathodes i4, the control grids I5, and the focussing electrodes iE. The three electron guns produce schematically represented beams Il, I8 and Iii by which to energize respectively, the blue, red and green phosphor areas of the screen I2. When these electron beams are properly converged in the plane of the masking electrode i3 they pass through the apertures thereof from different directions and impinge upon diiierent phosphor areas of the various groups so as to produce blue, red and green light. It is to be noted that the size of the phosphor areas, the angles between the beams and 'the spacing of the'mask i3 from the screen I2 as compared with the length of thetube are exaggerated for better illustration of the operation of the kinescope` The electron-optical apparatus of the kine scope l! also includes a beam-accelerating electrode consisting, in the present instance, or" a conductive Wall coating 2U formed on the inner surface of the tubular glass neck 2I of the kinescope extending from the region adjacent to the outer end of the focussing electrodes i6 to the conical section 22 of the tube which in this case is metallic. Suitable electrical connection (not shown) is made at the junction of the wall coating with the metal cone 22. Preferably, the target electrode structure, including the elec- `trode'l' and the luminescent screen l2 which for this purpose may be metallized, is electrically connectedto the metal cone 22 by suitable means (not shown). Metallization of a luminescent screen oi the character described may be eifected in the manner` disclosed in a paper by D. W. Epstein and L. Pensak titled Improved Cathode Ray Tubes with Metal-Backed Luminescent Screens published in the RCA Review, vol. VII, March 1946 at pages 5--10.

The described electrode structure of the kinesoope may be energized in a conventional manner such as that illustrated. The source of energy is represented by a battery 23 across the terminals of which there is connected a voltage divdel` Ell. The cathcdes Iii are connected to the grounded point of the voltage divider andthe controlvgrids I5 are connected to a. point which is somewhat negative relative to ground. Similarly, the focussing electrodes i6 are connected to a point on the voltage divider which may conventionally be at a potential of approximately 3000 volts positive relative to the grounded cathodes. Also the beam-accelerating anode, including the wall coating 20 and metal cone 22, is connected to the i voitage divider 2s ata point which may conventionally be approximately 18,000 volts positive relative to the grounded cathcdes.

The electron beams Il, I8 and I9 are modulated suitably in intensity under the control of color-representative video signals derived from a source Z5. vIt will be understood that the video signal source is represented herein entirely diagrammatically sinceit does not form an essential part of the present invention. The signal source 25 usually will be part of asignal receiver and may be understood to include a signal detector, or equivalent device, together with one or more stages of video signal amplification. Alternatively, the video signal source may be a color televisioncamera in the event that the kinescope I I is employed as a monitoigfor example. Also, it will be understood that the illustrated connection of the video signal source 25'to the electron guns of the kinescope II is merely diagrammatic and accordingly these connections may or may not be made directly to the cathodes Iii. Instead, it will be understood, thatthey may be made to the grids `I5 or,'in accordance with modes of operae tion of color image-reproducing apparatus, the video signal source may be connected both to the cathodes and to thecontrolv grids of the electron guns.

Also associated withv the'color kinescope II is a deflection yoke ewhichmay be entirely conventional including two pairs of suitably placed coils electrically connected together in such a manner that,when 'properly energized, electromagnetic ields are produced, whereby to effect both horizontal and-vertical-angular deiiections of the lelectron beams so as to scan the usual rectangular raster. Energization of the deflection coils comprising the yoke 26 may be eiected by conventional vertical and horizontal deflection wave generators 2l and 28, respective (see Figure e). Such apparatus will be understood to function suitably to produce substantially sawtooth energy at both horizontal and vertical delection frequencies so that the fields produced by the yoke 2E are varied in a substantially sawtooth manner.

The beam convergence system, in accordance with the present invention, also includes a plurality of electromagnetic iield producing elements such as the magnets 29 and 30 mounted around the neck 2| of the color kinescope adjacent to the predeiiection paths of the electron beam components. It is to be understood that the precise location of these magnets is not necessarily indicated in this iigure. Instead, as will appear in greater detail from a subsequent portion of the specification, it is to be understood that each of these magnets is located relative to one of the electron beam components so as to influence its associated beam component to the substantial exclusion of the others. Furthermore, it is to be understood that these magnets are of a character which, when suitably energized, produce respective iields which are transverse to the associated beam paths.

Each of these convergence electromagnets includes a pair of spaced pole pieces and at least one energizing winding. Preferably two windings are provided for each of the electromagnets for separate energization. These features will be described subsequently in greater detail.

Before describing the details of the convergence system with which the present invention is related, a brief description will be given of the general manner in which the apparatus functions to produce the desired results. The convergence magnets such as 29 and 3 are energized by substantially unidirectional energy so as to eiect an initial convergence of the electron beam components substantially in the plane of the apertured masking electrode i3. In order to do this, the unidirectional energization of these magnets is effected in such a way that the magnets may be individually energized in different magnitudes. lin eecting this initial beam convergence, it is to be understood that the beams may be in any desired one of their different deflected positions. For example, they may be initially converged at the center of the raster to be scanned. Alternatively they may be initially converged at one corner ci the raster.

The convergence magnets such as 29 and 30 also are dynamically energized by the control wave energy derived from a suitable generator (not shown in Figure 1) so as to effect a variation in the magnitude of the transverse fields produced respectively thereby. These field strength variations are in accordance with a predetermined function of the beam deflection. Variations in the strength of the fields produced by the convergence magnets such as 29 and 3U effect corresponding variations in the paths of the electron beam components relative to the longitudinal axis of the tube. Hence, suitable variations are made in the convergence angles between the various beam components so as to produce the desired convergence of the beam components substantially in the plane of the masking electrode I3.

For a further description of this type of beam convergence apparatus, reference now will be made to Figure 2 of the drawings. This figure shows more clearly the relative positions of the convergence magnets, such as 29 and 30 and, additionally, 3l, relative to one another and to the electron beams with which they are respectively associated. Inasmuch as all of these magnets are substantially the same, only one of them will be described in detail. The convergence magnet 29, which is associated with the blue electron beam Il, is provided with a core having a body portion 32 and two external pole pieces 33 and 3d. These pole pieces are mounted so as to be in close association with the tube neck 2|. Also, as indicated in Figure 1, the pole pieces extend for some distance longitudinally of they tube substantially as indicated. The magnet also is provided with an energizing coil structure 35 mounted upon the body portion 32. The energizing coil 3e preferably is provided with two windings, one for static energization and the other for dynamic energization in a manner to be described subsequently. The convergence magnet 2S produces a field which, in the vicinity of the electron beam il, is substantially transverse to the axis of the kinescope. By means of such a eld, the electron beam I l may be moved toward or away from the longitudinal tube axis. The direction and magnitude of such a beam movement is controlled by the energization of the magnet by means including the coil 35.

In Figure 2, it also is illustrated that for each of the magnets there are provided on the inside oi the tube neck 2i extended pole pieces so as to increase 'the eiiectiveness of these magnets. The magnet 2Q, for example, is provided with a pair ci' inwardly extending pole pieces 38 and isi, associated respectively with the external pole pieces 33 and 3G. By such means, it is seen that the reluctance of the magnetic circuit is considerably decreased, and also the flux distribution of the field produced between the internal pole pieces 35 and 3i is considerably improved.

With beam convergence apparatus of this general character, it may be seen from a further consideration of Figure 2 that such apparatus is adversely affected by leakage iiux from the delection yoke. Leakage deilection flux or a character to deflect the electron beam components Il, i8 and i9 to the left as viewed in the drawing is indicated by the broken lines 38. With respect to the internal pole pieces 3 and 3'! associated with the electromagnet 29, no adverse effects of the leakage deflection flux are produced. However, it is seen that the leakage de iiection iiux 3 passes between the internal pole pieces 39 and All of the electrcmagnet 3&3 substantially at right angles to these pole pieces since this is the path of lowest reluctance. Similarly, the leakage deflection flux 38 passes between the internal pole piecesl and @2 of the electromagnet 3| at right angles to these pole pieces. As a result, it may be seen that when the beams are being deflected to the left, the red beam i3 will be moved to a higher position than it would have in the absence or" the leakage flux from the deflection yoke, as indicated by the arrow. Similarly, the green beam i3 will have a lower than normal position when beam deflection is toward the left. Conversely, when beam deilection by the yoke is toward the right, as

viewed in Figure 2, the leakage flux 38 will be in the opposite direction, thereby tending to move the red beam downwardly and the green beam upwardly. Consequently, there is eected a misconvergence of the electron beam componentsas a result of the leakage flux from the delection yoke traversing the internal pole' pieces of certain of the convergence electromagnets.

In accordance with the present invention. there is provided means for preventing the leakage flux from the deflection yoke from adversely affecting the individual beam convergence electromagnets in the manner described. By referring again to Figure l and. also to Figure 3 of the drawings, this apparatus comprises a magnetic shield located between the deection yoke 26 and the convergence electromagnets, such as 29 andk 3i). In the illustrative form of the magnetic shield, it comprises a disk-like shielding member t3 of magnetic material mounted internally of the cathode ray tube. Preferably, the internal shielding member 43 has an outside diameter which enables it to flt snugly on the inside of the substantially cylindrical tube neck 2i. It also is provided with a centrally located aperture it so as to enable the passage of the electron beams. It is to be noted that the internal shielding member 43 has a substantial thickness` in the direction longitudinally of the tube axis. The magnetic shield also includes at least one other disk-like shielding member 45 of magnetic material located externally of the tube and in substantial alignment with the internal shielding member 3. The external shielding member has a centrally located aperture of proper diameter to enable it to be suitably mounted in close proximity to the outside of the tube neck 2|. The outside diameter or" the external shielding member i5 is made sufficient to effect the desired shielding. t is to be noted that the external shielding member L has a thickness longitudinally of the tube axis which is considerably less than that of the internal shielding member 43. The thickness of the external member should be sufficient to provide the necessary mechanical strength. Also, it may be arranged so as to enable a sliding adjustment thereof for varying the effectiveness of the shield. The external shielding member 45 is shown in solid lines in one extreme position at the back end of the internal member 13d and by dotted lines in a forward limiting position. Also, in accordance with the invention, the magnetic shield may include a plurality or external members such as 5 and d5.

The leakage ux from the deflection yoke 25, in the absence of the magnetic shield, is indicated as following generally the path 45. It is seen that this path links the electromagnetic convergence apparatus and produce the deleterious results previously described. By means of the magnetic shunt, the leakage ux may be confined substantially to the path indicated by the broken line 47. In this case, it is seen that the magnetic shield eectively shunts the leakage ux into a path which is harmless so far as the beam convergence apparatus is concerned.

Reference now will be made to Figure 4 of the drawings for a general description of an illustrative manner in which the beam convergence apparatus may be energized. The energizing coils of the convergence magnets 29, 3B and 3| include dynamic windings 48, i3 and 513` respectively. These convergence magnets also include static windings 5|, 52 and 53 respectively. The energizing circuit for the static convergence windings 5|, 52 and 53 includes a series circuit of resistors 51%, 55 and e5 connected between the positive terminal of a powerv supply and its load. Preferably, these resistors are adjustable so as to enable the individual control of the energizing current for the associated, static windings of the convergence magnets 29, 30 and 3|, respectively.

The dynamic windings 48, 49 and 5G of the convergence magnets 29, 30 and 3|, respectively, are connected in series with one another and to vertical and horizontal convergence wave generators 6l. and, 58, respectively. These convergence wave generators may be of the general type disclosed in the I. R. E. Friend paper o1' any other suitable forms. In general, the substantially sawtooth wave energy 5S) of eld frequency which is derived from a conventional vertical deflection Wave generator 2l for energization. of the vertical deflection yoke coils GS is converted by means of the vertical convergence wavel generator 5l into a substantially parabolic wave 5|. This parabolic wave energy is coupled by a capacitor 62 to the series connection of the dynamic windings of the convergence electromagnets. In a substantially similar manner, the line frequency sawtooth wave energy 53 derived from the horizontal deiiection wave generator 2.8 for the energization of the horizontal deilection yoke windings-E4 is converted by the horizontal convergence wave generator to a substantially parabolic wave E5 for impression by meansv including a coupling capacitor E55 upon the dynamic windings of the beam convergence electromagnets 29, 3D and 3|. By such means, it isseen that. theconvergence magnets are energized dynamically as functions of both vertical and horizontal beam deflection angles so as to effect substantial convergence of the electron beam components in the plane of the target electrode structure at all points in the scanned raster.

It, therefore, is seen from the foregoing description of an illustrative embodiment of the present invention that the leakage flux from a raster-scanning deflection yoke is prevented from reaching the region in which individual electronfiag-netsl are employed to effect static as well as dynamic convergence of a plurality of electron` beam components in the plane of a target electrode. The magnetic shield, in accordance withl the invention and by means of which the leakage: flux is shunted away from the convergence'apparatus, comprises in one form a plurality of disk-like members of magnetic material, one: of which is located inside of the cathode ray tube andk another of which is located outside of the. tube. It will be appreciated that, in some cases, satisfactory shielding may be effected by use of only one oi such members located either internally or externally of the cathode ray tube. Also, itlis to be noted that the shielding apparatus may be of a fixed or adjustable type as desired.

Ilhe nature of the invention, having been set forth in the foregoing description of an illustrative embodiment thereof, its scope is pointed out inthe appended claims.

What is claimed is:

1. In a cathode ray tube image-reproducing system wherein a plurality of electron beam components, which traverse pre-deection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deiiected both horizontally and vertically by electromagnetic beam deflection apparatus to scan a raster in a predetermined plane, electron beam convergence apparatus comprising, a plurality of electromagnets respectively mounted adjacent to said predeection beam paths and energizable to produce respective fieldsl transverse to said beam paths, each of said electromagnets having a core including a body portion located externally of said tube and a pair of pole pieces located internally of said tube and respectively extending from points adjacent to opposite ends of said body portion into the region of said associated beam component, and a magnetic shield located between said deiiection apparatus and said convergence electromagnets to exclude deflection flux from said electromagnets.

2. Electron beam convergence apparatus as dened in claim 1 wherein, said magnetic shield comprises a disk-like member located internally of said cathode ray tube.

, 3. Electron beam convergence apparatus as deiined in claim 1 wherein, said magnetic shield comprises a disk-like member located externally of said cathode ray tube.

4. Electron beam convergence apparatus as defined in claim 1 wherein, said magnetic shield comprises a plurality of disk-like members, one of said members being located internally of said cathode ray tube, and another of said members being located externally of said cathode ray tube.

5. Electron beam convergence apparatus as dened in claim 4 wherein, said internal and external disk-like members are relatively movable longitudinally of said cathode ray tube axis.

6. Electron beam convergence apparatus as delined in claim 5 wherein, said internal disk-like member has a greater dimension longitudinally of said cathode ray tube axis than the corresponding dimension of said external disk-like member.

'7. In a cathode ray tube image reproducing system wherein, a plurality of electron beam components, which traverse pre-deection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deilected both horizontally and vertically by electromagnetic beam deflection apparatus to scan a raster in a predetermined plane, and wherein a plurality of electromagnets each having' pole pieces located internally of said tube respectively adjacent to said pre-deflection beam paths and energizable to produce respective fields transverse to said beam paths by which to effect dynamic electron beam convergence, a magnetic shield located between said delection apparatus and said convergence electromagnets to exclude deflection flux from said electromagnets and comprising, a disk-like member oi magnetic material mounted internally of said tube and having a central aperture for the passage of said electron beam components, and a second disk-like member of magnetic material mounted externally of said tube in alignment with said internally mounted disk-like member and having a central aperture of suitable dimensions to accommodate said cathode ray tube envelope, said internally mounted member having a greater thickness longitudinally of said tube axis than the corresponding thickness of said externally mounted disk-like member, and said externally mounted member being adjustably positionable longitudinally of said tube axis to vary the effectiveness of said magnetic shield.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,332,881 Woerner Oct. 26, 1943 2,336,837 Bedford Dec. 14, 1943 2,457,175 Parker Dec. 28, 1948 2,611,099 Jenny Sept. 16, 1952

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